In fact I am not one of them as you are, but Nikon does make some interesting cameras.

1. build quality

Canon makes some good DSLRs, so does Sony. Pentax can be weather sealed which can be a plus.

2. brand

Again Canon, Sony SLT, and Pentax are recognized brands, but Canon is Nikon's biggest competitor in the brand name area.

3. many options for lenses

Well I could say Canon has a large choice in glass and Sony can use many older Minolta lenses.

4. mainly for professional or amateur work

Canon can be used for this as well, but so can Pentax and Sony.

5. other

I picked a Sony SLT A55 for my first camera to shoot with because I shot pictures Minolta when I was younger. I knew I could use some of the lenses I remember from my Minolta days, which are still quite good. I don't regret my choice in picking Sony. Nikon never crossed my mind in my decision when I got back into photography, but I did consider Canon heavily due to lens choice and briefly considered Pentax due to being weather sealed.